What should be blue is going green.
Global climate-change trends detected in indicators of ocean ecology [Link goes to Nature
Satellite remote sensing is the only means to obtain time series of marine ecosystems on a global scale, because it is the only way to obtain measurements at the required scales. Ocean-colour satellites, which measure the amount of light radiating from the ocean and atmosphere from Earth’s surface, have been collecting global measurements for decades. A great deal of research has focused on detecting long-term trends in ocean-colour data,
Remote-sensing data are available from https://oceancolor.gsfc.nasa.gov/l3; the specific data product names are the first 240 months of the monthly 9-km standard MODIS-Aqua Rrs at 412, 443, 488, 531, 547, 667, and 678 nm. Model outputs are available from https://doi.org/10.7910/DVN/08OJUV.
It is like when I look over the usually verdant green surrounding fields and find they are pale brown, I know that if it is not late September then there is a significant problem. We know this instinctively it is inbuilt. [since we live there and have the data readily available]
When I look out to sea, I am not so sure, it's not my habitual territory, what does the colour mean, do I have the right viewpoint?
Having remote satellite sensing allows the variations in the seasonal colour shifts to be easily visible making understanding [when given a colour chart] that much more visceral. The full analysis can then be better targeted to determine what the localized colour shifts mean and what is influencing them.
Some think that crystal-clear water is healthy, to others it means it is lifeless, only by analysis can this be proven one way or another.
Anyway I hope you found the article interesting,